Power conservation is a desirable attribute in a transceiver device, particularly a mobile or portable communication device, such as a cell phone, or a base transceiver station. Such devices may utilize an average power tracking (APT) mechanism or an envelope tracking (ET) mechanism. Cellular transmissions using protocols such as the Long-Term Evolution (LTE)-Advanced protocol (based on a 3GPP Release 10 specification released in March of 2011 and 3GPP Release 13, 2016 Update) may occur in time slots which, according to the LTE protocol, are 0.5 ms.
With the APT mechanism, a biasing voltage supplied to the power amplifier (PA) is selected based on a desired signal quality (linearity and/or efficiency) specified by the communication standard and is fixed during the time slot (but is changeable from slot-to-slot). This PA supply voltage value is set by a DC-DC converter, which takes the DC voltage supplied by a battery of the device and regulates it to a different value that may be used by the PA. The value is calculated based generally on a target output power level for that time slot. For example, if the target value (average power level) for sending the slot is 20 dBm, then a look-up table (LUT) may indicate that the DC-DC voltage should be fixed at 2.7 V for that time slot.
For envelope tracking, a fast DC-DC converter is used so that the supply voltage to the PA is adjusted to track the amplitude modulation signal, which helps reduce the power. However, depending on the characteristics of the output signal, use of ET is not always beneficial.